Questions

We built a simple model to model out each level of our conversion funnel: 1. Try 2. Registered 3. Pay. We realized given the same lift in percentage, the lower the conversion funnel, the bigger impact it makes on revenue. Is this true to most SaaS / eCommerce apps / sites?
If so, shouldn't we be focused much more effort bottom up?

Logically this makes sense. However is easier said than done, and many would argue that even if you aim for a bottom up approach you are in essence still going through the traditional model because you have to filter out anyway to get to your actual conversions.

Referrals are probably the best shortcuts there are but you still have that funnel approach.